1. Field of the Invention
The invention relates to drivers for Field Effect Transistors (FET), particularly of the Metal-Oxide-Semiconductor (MOS) power FET type (MOS FET). The invention has particular application in circuits where the FET source is not necessarily at a fixed voltage. Such applications include switching regulators for power supplies and power switches.
2. Description of the Prior Art
Present day power supplies traditionally utilize the switching regulator to provide voltage regulation and the MOS FET is often utilized as the pass element thereof. Generally, the N Channel FET exhibits superior "on" characteristics than the P Channel FET, thereby rendering the N Channel FET highly appropriate for use as the pass element in switching regulators. The low "on" resistance and zero gate current of the N Channel FET contribute to high efficiency of the regulator.
In order, however, to turn on the N Channel FET, a gate to source voltage of 10-15 volts is required. Thus, when the N Channel FET is utilized in a switching regulator, the gate must be driven to a potential 10 volts above the supply voltage. Prior art techniques to drive such devices in a switching regulator mode tend to be complex, costly and inefficient. Such prior art designs tend to utilize uncommon and expensive precision components, as well as additional power supplies to effect the drive voltage. Such designs tend to be awkward and are not readily integrated into a convenient monolithic Integrated Circuit (IC) format. The prior art designs generally operate over limited ranges of operating parameters such as primary supply voltage, operating frequency and temperature. Such prior art MOS FET drivers typically have undesirably large part counts and poor power efficiency.
For example, the prior art MOS FET driver designs include an auxiliary power supply 10 volts higher than the primary supply. This design tends to be expensive and inefficient. Another prior art design utilizes a floating 10 volt power supply referenced to the MOS FET source terminal. Such a design is very awkward and difficult to mechanize. A still further prior art design utilizes a remote power supply and such exotic components as an opto-coupler or an acoustic coupler. Another prior art design utilizes a transformer coupled signal to the gate that is referenced to the MOS FET source terminal. The capability of such an arrangement is limited to the particular design and/or application.
The MOS FET also has utility in power switches such as those utilized in space applications to conserve power by disconnecting non-critical subsystems from the power source. The drivers for such power switches suffer from the same disadvantages described above, with respect to the switching regulator.